In general, a front cover and a pump shell of fluid couplings (including torque converters) are welded to each other by arc welding. Therefore, a fluid coupling housing may be warped as a result of the welded portion being significantly affected by heat in combination with generation of a residual stress in the preceding pressing step. In the arc welding, in addition, welding metal such as a welding wire is added to the base material, and the welding metal may not be uniform over the entire circumference of the housing, which makes it troublesome to adjust the dynamic balance of the fluid coupling in combination with the warp due to the effect of heat.
There has hitherto been proposed a manufacturing method for a torque converter in which a front cover and a pump shell are welded to each other using a high-energy beam such as a laser beam or an electron beam (see Patent Document 1). In this technique, the outer peripheral side of one of the front cover and the pump shell is scraped as a first sheet, the other is superposed as a second sheet on the outer peripheral side of the first sheet with a predetermined gap, and a laser beam or the like is radiated at a gentle gradient with respect to a plane that faces the first sheet and the second sheet and such that the intense region of the beam is first applied to an edge portion (distal end surface) of the second sheet. Consequently, it is possible to establish such a temperature gradient in the thickness direction that the temperature is lower on the outer peripheral side for the first sheet, form such a temperature gradient in the thickness direction that the temperature is lower on the inner peripheral side for the second sheet, cause a thermal bending moment in the direction of decreasing the gap between the first sheet and the second sheet, and reduce the burden of adjusting the dynamic balance without using welding metal.